Nitrogen 11 History 9 Nonlinear optics 8 Nitrogen-fixing microorganisms 7 Motion pictures 6 Research 6 Soil Science and Agricultural Chemistry 6 Bacteriology 5 History and criticism 5 Mass media 5 Nitrogen-fixing plants 5 Philosophy 5 Plants 5 Social aspects 5 Social sciences 5 Bacteria 4 Legumes 4 Nitrogen fixation 4 Nitrogen fixing bacteria 4 Soil Biology 4 Sound 4 Television 4 Communication 3 Fiber optics 3 Nitrification 3 Nitrogen cycle 3 Nitrogen fixing trees 3 Remote sensing 3 Television viewers 3 Trees 3